This invention relates generally to semiconductor devices and to a method for their manufacture, and more specifically to a contact structure used in a semiconductor device and to a method for its manufacture.
In the fabrication of semiconductor devices, especially high density MOS integrated circuits, a significant amount of space on the integrated circuit die is used in making electrical contact between the semiconductor substrate and an overlying conductor layer or between two conductor layers overlying the substrate, or between a plurality of overlying layers and the substrate. The amount of area used for these contacts is minimized by using a "buried contact" or "shared contact." In a silicon gate MOS integrated circuit, for example, a buried contact achieves an electrical contact between the monocrystalline substrate and an overlying polycrystalline silicon interconnect by exposing a portion of the substrate and directly contacting that portion with an impurity doped polycrystalline silicon line. In a shared contact, the silicon substrate and a first overlying polycrystalline silicon pattern are electrically coupled together by a second level of polycrystalline silicon overlying the first.
Although the desirability of buried contacts or shared contacts is apparent from the amount of space which can be saved in the implementation of an integrated circuit function on a thin wafer of semiconductor material, the implementation of these contacts is not without problems. One of the major problems encountered in fabricating buried contacts or shared contacts is the pitting or etching of the underlying semiconductor substrate during the patterning of the overlying polycrystalline silicon lines. For example, in the conventional method for fabricating a buried contact, an oxide layer is grown on a silicon substrate and an opening is etched through that oxide layer to expose the intended contact area. A layer of polycrystalline silicon is then deposited over the oxide layer and extending through the opening to make contact with the silicon substrate. When the polycrystalline silicon layer is then patterned to form the necessary pattern of interconnecting lines, any over etching of the layer of polycrystalline silicon causes an etching of the underlying silicon substrate. Because the polycrystalline silicon in the contact openings is directly in contact with the silicon substrate, there is no etch-stop indicator which indicates when the etching of the polycrystalline silicon has been completed. The etchant for polycrystalline silicon is equally effective in etching the then exposed underlying substrate. A similar problem arises in the fabrication of shared contacts.
A need therefore existed for an improved contact and method for its fabrication which would overcome the problems attendant with the conventional fabrication of buried contacts and shared contacts.
It is therefore an object of this invention to provide an improved contact between first and second silicon structures.
It is a further object of this invention to provide an improved method for fabricating semiconductor devices including contacts between first and second silicon structures.
It is yet another object of this invention to provide an improved semiconductor device structure.
It is yet another object of this invention to provide an improved method for fabricating semiconductor devices.
It is a still further object of this invention to provide an improved means and method for electrically coupling between conductor levels of an integrated circuit.